This invention relates to an inductive angle sensor for a motor vehicle.
Potentiometers are still primarily used in motor vehicles as position sensors, specifically for determining displacement angles of motor controlled or regulated elements. Their advantage, namely that they are particularly inexpensive, is offset by the disadvantages of sensitivity to dirt accumulation and wear.
To avoid these disadvantages, increasing use is being made of non-contact angle sensors that operate according to magnetoresistive, capacitative, or inductive principles.
According to such a principle, an inductive angle sensor comprises an excitation coil with alternating current applied thereto, a magnetic field of which induces voltage in one or more receiving coils; an amplitude or phase relationship of this voltage being dependent upon a position of an inductive coupler that is movable relative to the coils.
Particularly in critical safety applications in motor vehicles, such as in determining an angular position of a throttle valve that can be adjusted by motor, redundant measuring sensors are provided for safety reasons. When a potentiometer is used as a sensor, a redundant measuring sensor can thus be designed simply as a double potentiometer.
A design of a redundant measuring inductive angle sensor is, however, problematic since a positioning of two inductive sensor systems in close proximity can result in mutual interference of the sensor system, particularly through overlapping magnetic fields generated by the exciting coils.
Consider an example of a redundant inductive angle sensor comprising two complete and independent sensor systems, up to an inductive coupling element whose position is to be sensed. If two sensor systems that are largely identical in design are used for this purpose, i.e. having two oscillators that apply alternating current of identical frequency on the exciting coils, beats occur, even at extremely low frequency deviations, in signals of the receiving coils, making evaluation of the receiving coil signals extremely difficult or even impossible.
One conceivable solution is to select extremely different oscillator frequencies so that possible difference frequencies can readily be filtered out. However, this would mean that the oscillator and the evaluation circuit, which can be advantageously combined respectively into one circuit, would have to be designed differently for the two sensor systems, which doubles development expenses. Additionally, a cost of producing two different circuits with a same number of pieces would be significantly higher than that of producing one switching circuit with twice the number of pieces.
Therefore an object of this invention is to provide a redundant inductive angle sensor that can be manufactured in a simple and most inexpensive manner and that excludes mutual interference between the sensor systems.